In recent years, there has been proposed adoption of organic EL (Electro Luminescence) panels that rely on electroluminescence phenomenon of organic materials as display panels for display devices such as digital televisions. A matrix of respective organic EL elements of the R, G, and B colors is arranged in a substrate of an organic EL panel.
It is important to increase light-extraction efficiency of the respective organic EL elements of the R, G, and B colors, from the standpoint of reducing power consumption, increasing service life of the organic EL panel, and the like. To this end, there has been proposed a number of arts for increasing light-extraction efficiency owing to creativity of optical design of the organic EL elements (see Patent Literatures 1 to 6). For example, Patent Literature 1 discloses that respective light-emitting elements of the R, G, and B colors are each constituted from a multilayer structure that is provided between a first electrode reflecting light and a second electrode transmitting light therethrough. The multiplayer structure includes a first layer generating holes, a second layer including a light-emitting layer of a corresponding color, and a third layer generating electrons. The first layer differs in film thickness among the R, G, and B colors (paragraphs 0022 to 0025). According to Patent Literature 1, light-extraction efficiency increases due to light interference phenomenon when the optical distance between the first electrode and the second layer is (2 m−1)/4 times a light-emitting wavelength, where m is an arbitrary positive integer (paragraphs 0026 and 0027).